Intergrown crystals: Mineral crystals that grow together like the pieces of a jigsaw
puzzle as magma cools to form igneous rocks.

On regents exams the phrase 'intergrown crystals' almost
always refers to igneous rocks although they may also be found in metamorphic
rocks. The size of the crystals is an indication of how long it took for the
rock to cool and may also indicate the location where the rock formed: